Comparative analysis of tracer studies in the determination of longitudinal dispersion coefficient.

The research presented in this paper is to determine the best tracer studies that will give acceptable estimates of longitudinal dispersion coefficient for Orashi river using rhodamine WT dye and sodium chloride as water tracer. Estimated results obtained for longitudinal dispersion coefficient for the case of rhodamine WT experiment ranges between 71 and 104.4 m2s-1 while that of sodium chloride experiment ranges between 20.1 and 34.71 m2s-1. These results revealed lower dispersion coefficient using sodium chloride as water tracer (WT) indicating that for larger rivers, sodium chloride should not be used as water tracer. The usage of sodium chloride as water tracer in the estimation of longitudinal dispersion coefficient is recommended in smaller streams as NaCl is relatively conservative. The established equations for both cases of investigation are proving satisfactory upon validation as degree of accuracy of 100.0% was obtained using discrepancy ratio (Dr). Standard error (SE), normal mean error (NME) and mean multiplication error (MME) of the developed equations is better when compared with other existing equations. However, Equation (17) is satisfactorily recommended.

An improved equation development for longitudinal dispersion coefficient.

The model developed in this paper is an improved equation for the longitudinal dispersion coefficient, which is an important parameter used to monitor and check the assimilatory capacity of rivers. This research incorporates total suspended solids (Ss) and total dissolved solids (Ds) to other selected functional parameters in order to investigate the contributions of Ss and Ds on the longitudinal dispersion coefficient. The results obtained from research indicates that the presence of Ss and Ds affects longitudinal dispersion coefficient as it reduces the magnitude of Dl values. The measured values of longitudinal dispersion coefficient estimated in this study vary between 71 and 104.4 m2 s-1. The percentage of Dr values estimated to be within 0.0 and 0.3 were 50.0% and within -0.3 and 0.0 were 50% for the developed equation and this indicates a degree of accuracy of 100.0%. While for Seo and Cheong, the percentage of Dr values determined to be within 0.0 and 0.3 were 63.3% and within -0.3 and 0.0 were 30% and gives a degree of accuracy of 93.3% and others are poor. SE, NME and MME results show a high accuracy for the derived equation revealing the adequacy of the derived equation in the estimation of D.

An efficient biosorbent for the removal of arsenic from a typical urban-generated wastewater.

The arousal of environmental concerns due to spike in environmental degradation has necessitated proper waste management and disposal. Arsenic, a potentially toxic element in cassava wastewater, requires treatment prior to the wastewater disposal to minimize environmental pollution and associated health implications. The present study thus addressed the treatment of As5+ heavy metal in cassava wastewater using an efficient biosorbent from chemically pretreated unshelled Moringa oleifera seeds. The effect of various factors influencing the biosorption process for arsenate removal was studied including pH, contact time, biosorbent dosage, and biosorbent pretreatment concentration. The results of Fourier transform infrared spectroscopy clearly suggested that additional functional groups attributed to esters were formed in the pretreated biosorbent, which is responsible for improvement in biosorption. It was found that contact time, biosorbent dosage, and biosorbent pretreatment concentration had statistically significant effect (p values < 0.05) on arsenate removal. A maximum percentage removal of 99.9% was achieved in the synthetic solution at pH 4.0, contact time of 30 min, and dosage of 2 g for biosorbent pretreated with 1 M of chemical solution. Furthermore, through isotherm and kinetics studies, it was discovered that the biosorption process for untreated biosorbent is by ion exchange, while that for treated biosorbents indicated a multifarious adsorption mechanism. Moreover, the biosorption process was exothermic and spontaneous. Also, it is noted that the sorption capability of the biosorbent increases with pretreatment concentration. A statistical model has been developed with prediction R2 of 0.898, which incorporates the effect of treatment concentration on the percentage removal of As5+ from cassava wastewater.

Optimal conditions for adsorption of zinc from industrial wastewater using groundnut husk ash.

Zinc is a toxic metal ion and is of importance in water and wastewater because it causes dizziness as well as lethargy when ingested by man. In the current study, the groundnut husk ash was investigated as a potential adsorbent for adsorption of zinc(II) ions from industrial wastewater. Groundnut husk ash was characterized by Fourier transform infrared spectroscopy, scanning electron microscopy and proximate analysis to identify the presence of the functional groups, surface morphology and the carbon content in the adsorbent respectively. To optimize the process parameters affecting the percentage removal of zinc(II) onto groundnut husk ash, the central composite design was used. The result of the optimization study showed an optimal percentage removal of 80.00%, with the optimal conditions of 1400 µm, 100 min, 25 °C, 40 mg/l and 20 mg for particle size, contact time, temperature, initial zinc concentration and adsorbent dosage respectively. The equilibrium data showed a better fit for Langmuir isotherm, when compared to Freundlich, Temkin and Dubinin-Radushkevich isotherms, with R2 of 0.965. The adsorption kinetics was best described by pseudo-second-order kinetics with R2 of 0.987. The thermodynamic study, on the other hand, showed a negative value of enthalpy change(∆H = - 27.021), indicating an exothermic as well as a spontaneous reaction, with the degree of spontaneity of the reaction ranging from - 55.487 ≤ ∆G ≤ - 56.427, which showed a corresponding increase in Gibb's free energy (∆G) with an increase in temperature.

A review on the applicability of activated carbon derived from plant biomass in adsorption of chromium, copper, and zinc from industrial wastewater.

Metal ion contamination in wastewater is an issue of global concern. The conventional methods of heavy metal removal from wastewater have some drawbacks, ranging from generation of sludge to high cost of removal. Adsorption technique for copper(II), zinc(II), and chromium(VI) using activated carbon has been found efficient. However, it is not economical on a large scale. This, therefore, necessitates the search for economical and readily available plant biomass-based activated carbons for the sequestration of the metal ions. This review presents the state of the art on the adsorption of copper(II), zinc(II), and chromium(VI) from industrial wastewater. Based on the literature review presented, the groundnut husk and corncob based activated carbons were found to possess the maximum adsorption capacities for copper(II), zinc(II), and chromium(VI) removal, when compared with the other plant biomass-based activated carbons. The high values of the adsorption capacities obtained were as a result of the isotherms and pH of the adsorbent as well as the initial concentration of the metal solutions. From the review, the equilibrium data fitted better with Langmuir and Freundlich isotherms than with other isotherms. Research gaps were identified which include a need to investigate the kinetic and the thermodynamic behaviors of the metal ions onto the studied adsorbents. Furthermore, a comparative analysis of the three types of activation of the adsorbents should be investigated using single and multi-metals. The optimization of particle size, contact time, temperature, initial concentration, and adsorbent dosage for adsorption of copper(II), zinc(II), and chromium(VI) onto the studied adsorbents using response surface methodology is equally required.